BEIRUT — A Syrian branch of al-Qaida on Tuesday claimed responsibility for multiple suicide attacks on security compounds in Damascus that killed at least five people in a weekend assault on the center of the regime's power.

The claim by Jabhat al-Nusra — its first in months — came as the U.N.'s special representative trying to end Syria's civil war said hopes for convening a peace conference next month are fading.

Jabhat al-Nusra claimed responsibility for Sunday's attacks in a statement posted on a militant website, warning Assad that his "criminal regime" should know that its fighters "do not fear any confrontation with the enemies."

The group said it sent seven suicide bombers wearing Syrian military uniforms to break into a police station in northern Damascus and a security compound in a southern district of the capital.

It also posted pictures claiming to show the attackers. Their faces blurred, the men are seen wearing military uniforms and holding Kalashnikov rifles as they sit on the ground with black Jabhat al-Nusra banners hanging behind them.

The Nusra Front has emerged as the most effective rebel force fighting to oust President Bashar Assad.

The group has claimed responsibility for some of the deadliest suicide bombings against Syrian government institutions and military facilities but was silent about its activities for at least two months — perhaps an indication that the group's success on the battlefield had become a source of friction with more moderate rebel groups as well as with al-Qaida leaders in neighboring Iraq.

The group's role in the Syrian conflict has been contentious within al-Qaida in the past months.

In April, the head of Iraq's al-Qaida arm announced a merger with the Syrian branch — a claim the Nusra Front's leader quickly rebuffed. Earlier this month, al-Qaida's global leader, Ayman al-Zawahiri, was quoted as trying to end the squabbling, insisting that the merger should be dissolved.

Tuesday's claim was signed by the Nusra Front — a possible indication that it has resumed operations on the battlefield as an autonomous group.

The group's affiliation with al-Qaida has significantly contributed to the reluctance of the opposition's Western backers to arm the rebels with heavier weapons.

More than 93,000 people have been killed since the Syrian conflict began in March 2011. It started as peaceful protests against Assad's rule but turned into a civil war after some opposition members took up arms to fight the government's harsh crackdown on dissent.

Partly because of opposition disarray, even the most modest international efforts to end the Syrian conflict have failed.

In Switzerland, U.N.'s special envoy to Syria, Lakhdar Brahimi, told reporters he still hopes international negotiations to find a political solution to the conflict can be convened in Geneva — but not until later in the summer.

"Frankly now, I doubt whether the conference will take place in July," he said, noting that the Syrian opposition is not meeting until early July and probably would not be ready.

"Since our previous meeting here on the 5th of June, the situation on the ground in Syria has hardly improved. It is still relentless destruction, killing, more suffering, more injustice, and more uncertainty for the future of the Syrian people," Brahimi said.

Brahimi was mediating a meeting between the U.S. and Russia, which are at loggerheads over the conflict.

Russia supports the Assad regime and Washington has backed the opposition, which insists Assad should relinquish power. Assad has repeatedly dismissed demands to leave power and said he has the right to run for another term in next year's presidential elections.

In Saudi Arabia, U.S. Secretary of State John Kerry insisted that an international conference be convened to end the bloody civil war.

"We believe that the best solution is a political solution," Kerry said after meetings with Saudi Foreign Minister Prince Saud al-Faisal in the capital, Riyadh. Saudi Arabia is a key U.S. ally in the Middle East.

In violence Tuesday, government troops fought rebels in the Damascus suburb of Qaboun, residents and activists said, as the regime tries to push opposition forces further away from the capital, the seat of Assad's power.

The Britain-based Syrian Observatory for Human Rights said there was also fighting in rebel-held districts of Eastern Ghouta near Damascus.

Also Tuesday, Assad approved a law to punish those entering Syria illegally with a prison sentence ranging from one to five years and a fine of five to 10 million Syrian pounds ($50,000 to $100,000) according to state-run SANA news agency. The decree appears aimed at cracking down on merchants and smugglers bringing goods over Syria's border with Turkey without paying customs.

Syria's border posts with Turkey have been under opposition's control since the rebels took much of the north in an offensive last summer.

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Associated Press writers John Heilprin in Geneva, Qassim Abdul-Zahra and Sinan Salaheddin in Baghdad contributed to this report.

A South Pacific cruise was interrupted by brawls apparently caused by a 23-member family who threw punches at other passengers, some of whom said they locked themselves in cabins to escape three days of violence.